Titus Livius (Livy), The History of Rome, Book 1
Rev. Canon Roberts, Ed.

20. Next he turned his attention to the appointment of priests. He himself, however, conducted a great many religious services, especially those which belong to the Flamen of Jupiter.¹ But he thought that in a warlike state there would be more kings of the type of Romulus than of Numa who would take the field in person. To guard, therefore, against the sacrificial rites which the king performed being interrupted, he appointed a Flamen as perpetual priest to Jupiter, and ordered that he should wear a distinctive dress and sit in the royal curule chair. He appointed two additional Flamens, one for Mars, the other for Quirinus, and also chose virgins as priestesses to [3] Vesta. This order of priestesses came into existence originally in Alba and was connected with the race of the founder. He assigned them a public stipend that they might give their whole time to the temple, and made their persons sacred and inviolable by a vow of chastity and other religious [4] sanctions. Similarly he chose twelve ‘Salii’ for Mars Gradivus, and assigned to them the distinctive dress of an embroidered tunic and over it a brazen cuirass. They were instructed to march in solemn procession through the City, carrying the twelve shields called the ‘Ancilia,’ and singing hymns accompanied by a solemn dance in triple time.

The next office to be filled was that of the Pontifex [5] Maximus. Numa appointed the son of Marcus, one of the senators —Numa Marcius —and all the regulations bearing on religion, written out and sealed, were placed in his charge. Here was laid down with what victims, on what days, and at what temples the various sacrifices were to be offered, and from what sources the expenses connected with them were to be [6] defrayed. He placed all other sacred functions, both public and private, under the supervision of the Pontifex, in order that there might be an authority for the people to consult, and so all trouble and confusion arising through foreign rites being adopted and their ancestral ones neglected might be [7] avoided. Nor were his functions confined to directing the worship of the celestial gods; he was to instruct the people how to conduct funerals and appease the spirits of the departed, and what prodigies sent by lightning or in any other way were to be attended to and expiated. To elicit these signs of the divine will, he dedicated an altar to Jupiter Elicius on the Aventine, and consulted the god through auguries, as to which prodigies were to receive attention.